Preparation of hydrocarbons

ABSTRACT

A charge aromatic stream, such as a C6-C12 stream, is typically treated to separate out an intermediate C7-C8 aromatic stream. The light stream, e.g. benzene, is transalkylated with the C9-C12 component of the charge to form additional C7-C8; and excess C9C12 (over and above that used in transalkylation) is dealkylated to C6-C8. The C6 portion of the dealkylate is used in transalkylation.

United States Patent Suggitt et al.

[ Dec. 16, 1975 [5 PREPARATION OF HYDROCARBONS 2,399,781 5/1946 Arnold 260/672 2,480,939 9/1949 Lee et al 260/672 [75] Inventors X21 22? 3,249,645 5/1966 Suld 260/672 eepsie, b 0th of N Y Primary ExaminerDelbert E. Gantz [73] Ass1gnee: Texaco Inc., New York, NY. Assistant Examiner-C. E. Spresser 22 Attorney, Agent, or FirmT. H. Whaley; C. G. Ries; 1 l 6 July 1974 Carl G. Seutter [21] Appl. No.: 485,859

[57] ABSTRACT 52 US. Cl. 2 1 60/672 260,672 g g A charge aromatic stream, such as a C C stream, is 51 1m. (:1. c070 3/58 typically treated fi f?f imemegiate fi 58 M f u aromatic stream. e 1g t stream, e.g. enzene, 1s 1 0 Search 260,672 672 672 R transalkylated with the C C component of the 56 charge to form additional C -C and excess C -C g g zf g gz (over and above that used in transalkylation) is dealkylated to C -C The C portion of the dealkylate is 2,383,072 8/ 1945 Oblad 260/672 used in transalkylation.

2,389,713 11/1945 Atwell 260/672 2,399,780 5/1946 Arnold 260/672 11 Claims, 3 Drawing Figures US. Patent Dec. 16, 1975 Sheet 2 of 3 3,927,135

US. Patent D60. 16, 1975 Sheet3of3 3,927,135

PREPARATION OF HYDROCARBONS FIELD OF THE INVENTION This invention relates to the preparation of hydrocarbons. More specifically it relates to a process for recovering toluene, or C aromatics, from aromatic feeds containing benzene, toluene, and C C Cm. and C aromatics.

BACKGROUND OF THE INVENTION As is well known to those skilled-in-the art, during processing of petroleum-derived fractions there may be obtained various aromatic fractions containing C C C C and higher cuts. One typical aromatic fraction which may be so obtained contains predominently aromatic hydrocarbons having 6-ll carbon atoms. Still another aromatic fraction which may be obtained, referred to as crude xylenes, actually contains hydrocarbons having 7-9 carbon atoms.

Refinery operations in which high grade gasolines are to be produced may recover aromatic fractions containing predominantly 6-8 carbon atoms referred to as a BTX fraction containing substantial quantities of benzene, toluene, xylenes, and ethylbenzene.

In processing each of these fractions, it is commonly desired to recover each of the components to permit most efficient utilization of the separated components. In the case of the crude xylenes, it may be desirable to recover substantially pure xylenes free of C and C cuts.

In the case of the C -C charge, it may be desirable to recover the toluene and C aromatics to permit e.g. use in gasolines and to thereby upgrade the latter in particular to increase the back end' volatility which improves the drivability of new cars during engine warrnup. More particularly the possibility of more severe restrictions on the end point of motor naphtha raises a problem which may be solved by the presence of increasing proportions of toluene and C aromatics in motor fuels with decreased proportions of benzene and C to C aromatics.

It is an object of this invention to provide a process for treating a charge aromatic hydrocarbon stream containing a heavier component, a middle component, and a lighter component to permit recovery of the middle component. It is another object of this invention, in certain of its embodiments, to provide a process for treating an aromatic stock containing C to C aromatics to permit recovery of toluene and C aromatics and to process, substantially to extinction, the C to C and the benzene. It is another object of this invention to provide a process for treating a charge BTX stream to permit substantial recovery of toluene with conversion, preferably substantially to extinction, of the benzene and xylene components to yield additional toluene. Other objects will be apparent to those skilled in the art.

STATEMENT OF THE INVENTION In accordance with certain of its aspects, the method of this invention for treating a charge aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component having a larger number of carbon atoms than does said middle component, and (iii) a lighter component having a smaller number of carbon atoms than does said middle component may comprise stream containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component thereby forming a transalkylate stream containing said middle component;

d. recovering said middle component from said transalkylate stream;

e. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier component, a middle component, and a lighter component;

and

f. recovering said middle component from said dealkylate stream.

DESCRIPTION OF THE INVENTION The process of this invention may preferably be used to treat a charge containing a significant proportion of aromatic content; and such charge stocks may be prepared typically by extracting aromatic components from the effluent from a reforming operation.

The feed to a reforming operation, typically a catalytic reforming operation, may be a naphtha, preferably a straight run naphtha such as a full boiling range naphtha derived from atomspheric pressure distillation of crude oil in a crude topping unit.

Typically a feed naphtha stream may be characterized by the following illustrative criteria:

Broad Range Property Typical API Gravity 45-75 62 IBP F 40-l 50 100 EP F 225-400 350 RON Clear 30-70 56 Aromatics vol. 7: 0-90 5 Naphthenes vol. 7: 0-90 40 Paraffins vol. 7: 3-90 55 Olefins vol. 7: 0-50 0 In a preferred embodiment the feed naphtha may be passed to a reforming operation, preferably a catalytic reforming operation, wherein reforming is carried out at 850-975F, say 920F at 0-800 psig, say 300 psig with a WHSV of 10-10, say 2.8 and a hydrogen to hydrocarbon mole ratio of 2-10, say 7. The preferred catalyst may be e.g. a noble metal on alumina, typically 0.4% Pt-0.2% Rhenium.

Reformate may be characterized by the following criteria:

Property Broad Range Typical API Gravity 35-60 45 IBP F -150 1 10 EP "F 350-450 410 RON Clear 80-105 Aromatics vol. 9: 30-75 68 -continued Property Broad Range Typical Naphthenes vol. 7: -20 4 Paraffins vol. 7: l0-60 28 Olefins vol. 7! 0-5 0 The reformate is passed to a separation operation, preferably an extractive distillation operation, typically a Udex unit, wherein aromatics may be separated from nonaromatics. Reformate may for example be contacted with aqueous glycols to permit attainment of aromatic extract characterized by the following crite- Property Broad Range Typical API Gravity" 30-60 33 lBP "F 176-300 176 E? F 250-425 410 Aromatics vol. /1 80-l00 99 Naphthenes vol. 7: 0-5 1 Puraffins vol. 7: 0-l0 0 Olefins vol. 7E

Although such a charge aromatic stream may be typical of those which may be treated by the preferred process of this invention, other streams containing hydrocarbons having 6-12 carbon atoms may be employed-such as those characterized by the following The charge stream contains a middle component as well as heavier and a lighter component, the latter having respectively a larger number and a smaller number of carbon atoms than does said middle component. Thus the charge stream may contain a benzene light component, a tolue'ne middle component, and an ethyl benzene heavy component. In one embodiment, the heavier and lighter components may contain respectively more and less alkyl groups than does the middle component. Such a system may include e.g. benzene, toluene, and methylethylbenzene as lighter, middle, and heavier components. In the preferred embodiment however, the several components may contain the same alkyl group (e.g. methyl); and the lighter component may contain a smaller number of alkyl groups (e.g. none as in the case of benzene) and the heavier component may contain a large number of alkyl groups (e.g. 2-3 as in the case of xylenes plus trimethylbenzenes than does the middle component typically toluene.

in practice of the process of this invention, in accordance with certain of its aspects, the charge aromatic hydrocarbon stream, commonly containing (i) l-lO moles, say 2 moles of a lighter component typically benzene, (ii) 0-20 moles, say 8 moles of a middle component, typically toluene, and (iii) 3-20 moles, say 12 moles of a heavier component, typically xylenes, is passed to a separation operation wherein the charge stream is separated into lighter, middle, and heavier streams containing the lighter, middle, and heavier components.

In a preferred embodiment, this is carried out in a distillation operation wherein for example in a first charge tower there may be recovered as bottoms, a stream containing the heavier component. The overhead, containing the middle component and the lighter component, may be further distilled to produce bottoms containing the middle component and overhead containing the lighter component. In an alternative embodiment, the first tower overhead may be lighter component the distillation of the bottoms therefrom in a second tower producing heavier component as bottoms and middle component as overhead. In a further alternative embodiment, this separation may be carried out in one tower with sidestream stripping to obtain the desired three products which in the preferred embodiment may be essentially benzene, toluene, and xylene.

In typical operation, there may be obtained 3-10 moles, say 8 moles of a first stream containing the lighter component and having the following character- 1stics:

Component Broad Typical Benzene wt. 7: 60-100 90 Toluene wt. 0-30 10 Xylene wt. 7: 0-l0 0 Other 0-l 0 There is also obtained 10-50 moles, say 20 moles of a second stream containing the middle component, and having the following characteristics:

Component Broad Typical Benzene wt. 0-20 v I 5 Toluene wt. 7c lO-l00 Xylene wt. '7: 0-20 5 Other 0-l 0 There is also obtained 10-50 moles, say 30 moles of a third stream containing the heavier component and having the following characteristics:

Component Broad Typical Benzene wt 7: 0-l0 0 Toluene wt 7: 0-20 l0 Xylene wt 7: 70-l00 90 Other tion be maintained so that the charge preferably con-' tains an equivalent amount of heavier component per mole of lighter component, typically bout 1.1-1.2, say 1.1 moles of xylene per mole of benzene charged to transalkylation. This permits generation of a product toluene which desirably contains benzene in substantially decreased quantities.

For example under otherwise comparable conditions (when the same amount or concentration of toluene is produced) the amount of benzene in the product transalkylate when the equivalent mole ratio In is e.g. 1.1 may be only 60% of that present when the mole ratio is e.g. 0.7. Thus operation at mole ratio m of e.g. 1.1 permits ready separation of toluene from the decreased quantity of benzene; and it permits increase in the proportion of xylenes in the system which when recycled, as in the preferred embodiment, permits maintenance of a third stream containing more e.g. xylene than the equivalent amount as defined supra.

When heavier streams such as C C C aromatics are used to transalkylate with benzene to generate toluene, then the ratio of benzene to heavy aromatic stream should be such that the ratio m of the total number of alkyl (e.g. methyl) groups to aromatic rings should be about 1.1 to 1. If xylenes are to be the preferred transalkylation product, then the ratio m of the total number of methyl groups to aromatic rings should be about 2.1 to 1.

It is noted that the typical composition of the preferred charge composition, viz. an aromatic extract from reformate, commonly also contains more moles of heavy component e.g. xylene than is equivalent to the benzene as defined supra. This may be because typically reforming as commonly carried out, produces substantially more of the heavier (e. g. xylenes) fraction than it does of the lighter (e.g. benzene) fraction.

Charge to transalkylation thus includes typically 5-20 moles, say 10 moles of the first stream containing lighter components, preferably a stream of substantially pure benzene and 5-25 moles, say 12 moles (the equivalent amount) of the first portion of the third stream containing heavier components, preferably a stream of substantially pure xylene.

Transalkylation may be carried out at a wide range of conditions. It may for example be preferably effected at 500l200F, more typically 500850F, say 625F and l002000 psig, say 800 psig at Ll-lSV of l-l5, say 4 with hydrogen to hydrocarbon mole ratio of 2-15, say 4. Catalyst is preferably 85% alumina matrix plus 15% cobalt sulfide on 40:1 SiO :Al O;, acid leached mordenite. 0.5% sulfur (as H 5) is present in the hydrogen stream.

Alternatively with a 0.75% platinum on fluorided alumina (36%F), transalkylating conditions may typically be 8501l50F, say 1000F and 100-1000 psig, say 300 psig at LHSV at 05-10, say 2 with hydrogen to hydrocarbon mole ratio of 2-15, say 6.

The transalkylate may typically contain 5.7 moles of a lighter component, preferably benzene, 8.7 moles of a middle component, preferably toluene, and 6.6 moles of a heavier component, including e.g 5.4 moles of xylenes and 1.2 moles of C C The transalkylate is separated into the three components, either in the same separation (eg distillation) operation as that in which the charge hydrocarbon stream is separated or alternatively in a separate separation operation. Regardless of which of these alternatives is employed, the middle component may be recovered as product and preferably at least a portion of the lighter (and in certain instances, of the heavier) component may be recycled, after separation, to the transalkylation operation.

The second portion of the third stream (obtained during the separation of the charge) which contains the third component in amount over and above that which is equivalent to the quantity passed to transalkylation, is passed to dealkylating operation. This stream, containing 10-40 parts, say 10 parts of e.g. substantially pure xylene, plus lesser quantities of heavier components in one embodiment, may preferably be mixed with at least a portion of the heavier component (typically xylene in the preferred embodiment) recovered from the transalkylate in amount of say 6.4 parts. This mixing may be effected by mixing the two heavier streams each separately recovered or preferably by recovering them in a common separation (eg distillation system).

The total charge to dealkylation typically includes 16.6 parts of the several streams consisting essentially of the heavier components. It may in the preferred embodiment contain the following:

Component Broad Parts Preferred Benzene 0-2 Toluene 0-5 0 Xylene 5-65 15.2 C to C, aromatics 0-5 1.4

Component Broad Parts Typical Benzene 51 5 8 Toluene 1- l 0 6 Xylenes l-lO 2.6

and heavier This dealkylated stream, containing. lighter, middle, and heavier components is passed to a separation operation, preferably a distillation operation, wherein a lighter fraction is recovered having the following typical characteristics:

Component Broad Parts Typical Benzene 5-8 7.8 Toluene 0-3 0.2 Xylenes 0-1 0 and heavier There is also recovered from the dealkylated stream a middle fraction having the following typical characteristics:

Component Broad Parts Typical Benzene 0-3 0.2 Toluene 3-6 5 .6 Xylenes 0-3 0.2

and heavier There is also recovered from the dealkylated stream a heavier fraction having the following characteristics:

Separation of the dealkylated stream into its component portions preferably (i) a stream containing the lighter component, (ii) a stream containing the middle component, and (iii) a stream containing the heavier component may be effected in one distillation tower or in two distillation towers as in the case of the initial separation of the charge aromatic stream to the first separation noted supra.

In one preferred embodiment, the dealkylated stream leaving the dealkylation operation may be recycled to and combined with the charge aromatic hydrocarbon admitted to the first separation operation. Thus both of these separations may be, and preferably are. carried out in the same separation operation.

The stream (containing the heavier component) recovered from separation of the dealkylate is preferably passed to transalkylation wherein it is mixed with the charge and transalkylated with the stream (containing the lighter component) recovered from the dealkylate and from the first separation. In practice of the process of this invention in the preferred embodiment, there is passed to the transalkylation operation substantially all the benzene recovered in the total system such as that recovered from the first separation, from the distillationseparation of the dealkylate, and from the distillationseparation of transalkylate when the separation is effected in three steps.

In a preferred embodiment. the amount of xylene charged to transalkylation may preferably be l.l-l.2 moles per mole of benzene.

The proportion of the total of the heavier fraction which is'passed to dealkylation and the proportion which is passed to transalkylation may depend upon the operating parameters of the system and particularly upon the relative composition of the initial charge and the operation of the dealkylation and transalkylation steps and the products desired. In the preferred embodiment, there may be more heavy components within the system than the equivalent amount necessary to transalkylate the light component to produce the desired middle component; and the excess of heavy component over that equivalent is charged to the dealkylation reaction. In another embodiment, where the heavy component is present in the equivalent amount, it may not be necessary to carry out the dealkylation step. In still another embodiment, the heavy component may be present in less than equivalent amount; and in this instance the dealkylating step may be omitted and a portion of the lighter component may be bled ofi to permit maintenance of equivalency. It will also be apparent to those skilled in the art that lighter or heavier component may be provided from outside sources to permit proper functioning of the transalkylation operation. In any event it is a feature of the process of this invention in its preferred embodiment that dealkylation may preferably be employed to convert at least a portion of the heavier component (normally present in excess) to dealkylated components and to thus maintain a balance in the system.

For purpose of illustration in typical overall operation of the novel process of this invention, it may be possible to convert a charge stream parts by weight) containing eg 10 parts by weight of toluene, 40 parts by weight of xylenes, and 50 parts by weight of trimethylbenzenes into a product stream containing a total of 95.5 parts by weight of substantially pure xylenes. Although in practice, it may be desirable to provide a bleed to remove some of the undesirable very light or very heavy by-products or to add some eg trimethylbenzene or toluene to balance the system, it is a feature of the process of this invention that the system is usually sufficiently balanced that in normal operation there may be no need for such steps.

According to certain of its aspects, the novel process of the invention may be carried out in the process flow sheets schematically set forth in the drawings. It will be apparent to those skilled in the art that the representation is schematic and that it does not show various condensers, reboilers, pumps, collection vessels, etc. or details of processing steps.

FIG. 1, illustrates a system used for the recovery of aromatics according to the disclosed process.

FIG. 2 illustrates an alternative system for the pro cess.

FIG. 3 illustrates the preferred system for operation of the process.

In FIG. 1, charge in line 10 includes a naphtha stream which is reformed in reforming operation 11. Reformate is passed through line 12 to extracting operation 13 (typically a Udex separation unit) wherein an aromatic extract is produced and withdrawn through line 14. Undesired rafiinate may be withdrawn through a line not shown. The stream in line 14 consists essentially of benzene, toluene, and xylene and heavier in the preferred embodiment.

The BTX stream in line 14 is fractionated in charge tower 15 from which 430 parts of bottoms (substantially pure xylene) are withdrawn through line 16. Overhead, containing benzene and toluene, is withdrawn through line 17 and passed to charge benzene fractionator 18. Toluene in amount of 450 parts is withdrawn through line 19; and parts of benzene are withdrawn through line 20.

The benzene in line 20 may be combined with that in line 21 and the resultant 439 parts of benzene are passed through line 22. They are joined by 713 parts of xylene from lines 16, 23, 24 and optionally line 25; and the resultant charge to transalkylation in line 26 contains l.l methyl groups per benzene ring. Make-up or draw-off of xylenes may be effected if desired through line 27; and make-up or draw-off of benzene may be effected if desired through line 28.

Transalkylation is effected in transalkylation operation 29; and the transalkylate in line 30 may contain 260 parts of benzene, 471 parts of toluene, 339 parts of xylene, 74 parts of C and 8 parts of C and heavier. This mixture is passed to transalkylate tower 31 wherein there is produced 421 parts of xylene and heavier bottoms recovered through line 32 and over head recovered through line 33. Overhead is distilled in transalkylate benzene fractionator 34 from which 471 parts of toluene bottoms are recovered in line 35 and 260 parts of benzene overhead are recovered in line 36. The latter stream may be recycled to transalkylation through line 37.

The 339 parts of xylene in the bottoms in line 32 may be recovered by fractionation and recycled in whole or in part through line 25 to transalkylation. In some embodiments. it may be desirable to treat the xylene bottoms (as by distillation) to separate C and heavier therefrom prior to recycling through line 25. When this is done, the 82 parts of C and heavier may be routed through line 38 to dealkylation together with the xylene in line 23 from bottoms line 16.

Bottoms from the transalkylate benzene fractionator 31 in line 32 minus the xylene in line 25 will be passed in typical total amounts of 82 parts of Q, and heavier and 56 parts xylene through line 38. Here it may he joined with parts of xylene from line 39. and the mixture passed through line 40 to dealkylation operation 41.

Dealkylate in line 42, containing 59 parts of benzene, 44 parts of toluene. and l() parts of xylene and heavier. is passed to dealkylate tower 43. 10 parts of xylene bottoms recovered therefrom are passed through line 39. Overhead is passed through line 44 to dealkylate benzene fractionator 45. Toluene bottoms are withdrawn therefrom through line 46 in amount of 44 parts. 59 parts of benzene overhead are withdrawn as overhead through line 47 and joined with the stream in line 37. being recycled to transalkylation. It will be apparent to those skilled in the art that each of the groups of distillation columns 15, I8 and 3|, 34 and 43, 45 may be operated so that the first of each group produces benzene overhead and toluene-xylene bottoms and the second of each group produces toluene overhead and xylene bottoms. In a preferred embodiment. there may be a third tower in each group to separate C and heavier from the xylenes prior to further use eg transalkylation or dealkylation of this latter stream.

In FIG. 2 of the drawing. there is disclosed an alternative mode of carrying out the process according to practice of this invention.

The general characteristics of the processing steps and the units in which they may be carried out are comparable in some respects to those set forth in FIG. 1; and accordingly the items are numbered to correspond with items in FIG. 1. It is a feature however of the processing train of FIG. 2 that the dealkylate in line 42 is recycled through line 49 or more preferably through line 50 so that separation into the desired components occurs in towers 31 and 34 or more preferably in towers l5 and 18.

This unexpectedly permits elimination of the capital and operating costs of towers 43 and 45 shown in FIG. 1

The preferred mode of operation of the process of this invention is however set forth in FIG. 3 of the drawing. The general characteristics of the processing steps and the units in which they may be carried out are comparable in some respects to those set forth in FIG. 1; and accordingly the items are numbered to correspond with those in FIG. I.

It is however a feature of the processing train of FIG. 3 that the distillation separation into light streams, middle stream. and heavy streams is carried out in a single distillation operation including two towers. It will be apparent that towers 31, 34. 43 and 45 of FIG. 1 have been eliminated and that processing is carried out in only two towers l5 and 18.

The transalkylate in line 30 of FIG. 3 is recycled through line 50 and is mixed with the stream in line 14 passing to tower l5. Similarly the dealkylate in line 42 is recycled through line 50 in comparable manner.

It is readily apparent that the processing train of FIG. 3 is characterized by a high degree of efficiency and by a minimum of capital and operating costs. The ability of such a system to readily convert aromatic charge stocks to desired products and to separate these desired products (in a system which produces little or no byproducts in normal operation) is conducive to operation under very economic conditions.

terized as follows:

Property Value API Gravity n2 IBP "F IOU EBP F 350 RON (lear 5h Aromatics vol. '71 5 Naphthenes vol. '7'

Parallins vol. '71 ()lefins vol. /1 0 Catalytic reforming is carried out in operation ll at average temperature of 920F and 300 psig with a WHSV of 2.8 and a hydrogen to hydrocarbon mole ratio of 7. The catalyst is 0.375% platinum ().2% rhenium on alumina.

Reformate in line 12 is characterized as follows:

Property Value API (Iravity 45 IBP F 11o EBP "F 420 RON Clear 99 Aromatics vol. 7! 68 Naphthenes vol. '/r 4 Paraffins vol. '7: 28 Olefms vol. '7: (I

The reformate is passed to Udex separation operation 13 wherein it is contacted with aqueous glycol to permit attainment in line 14 of an aromatic extract characterized by the following criteria:

Component Parts by Weight Benzene 5 Toluene 20 Xylenes 4O -C aromatics 37.5

The stream in line 14 is mixed with the stream from line 50 to form a mixed stream which. in this embodiment. contains:

Component Parts by weight Light ends 15.07 Benzene 37.10 Toluene 87.43 Xylenes 70.91 C,,C aromutics* 45.18 255.69

*contains ethyl derivatives as well as methylhenzenes The light ends are flashed off in a tower, not shown, and the 240.62 parts of C 41,, aromatics in the combined streams from lines 14 and line 50 are admitted to fractionation operation 15. Overhead recovered in line 17 contains 37.10 parts of benzene and 87.40 parts of toluene.

The benzene-toluene fraction in line 17 is admitted to benzene fractionator 18. Net bottoms in line 19 contain 87.43 parts of toluene in purity greater than 99%.

Overhead from benzene fractionator 18, recovered in amount of 37.10 parts (containing benzene of purity greater than 99%) in line 20, is passed through lines 20, 22 and 26 to transalkylating operation 29.

The bottoms from fractionation operation are withdrawn in amount of 1 16.09 parts of C C aromatics, through line 16. (If desired, a portion may be bled off through line 27). This stream is passed through line 23; and 47.80 parts thereof are passed through lines 24 and 26 to transalkylating operation 29.

In transalkylation operation 29, 37.10 parts of benzene from line 22 and 47.80 parts of xylene from line 24 (representing a 1.1: 1 mole ratio of methyl groups to benzene rings) are transalkylated at 600750F, say 725F and 1000 psig, 4 Ll-ISV and 4:1 hydrogen to hydrocarbon mole ratio. Catalyst contains as active component 15% of a 40:1 SiO :Al O acid leached mordenite bearing cobalt sulfide in 85% of alumina matrix. Effluent in line 30 contains 84.90 parts of product containing near equilibrium conversion of 4042% toluene. Y

Specifically the product in line 30 contains 0.88 parts of light ends, 19.32 parts of benzene, 33.72 parts of toluene, 24.54 parts of xylenes and 6.44 parts of C C aromatics. This stream is recycled through line 50 to line 14.

In common practice of the process of this invention, the stream in line 23 will contain more C -C aromatics than is needed to transalkylate the benzene in line 22; and this excess of C C aromatics, 68.29 parts (containing 41.71 parts of xylenes and 26.58 parts C -C aromatics,) is passed through line 40 to dealkylating operation 41. (If the amount of C -C in line 23 is less than that needed to transalkylate the benzene in line 22, then either xylene from an external source may be admitted to line 23 as through line 27, or benzene may be withdrawn through line 28.) If the C C in line 23 contains the correct number of methyl groups (eg 1.1 methyl for every aromatic ring in the combined benzene plus C -C stream) which is equivalent to the benzene in line 22, then the transalkylation step may be omitted.

In this preferred typical embodiment, 68.29 parts of C -C in line 40 are passed to dealkylating operation 41 wherein dealkylation is effected at l100-l300F say 1200F and 300-500 psig, say 400 psig for 05-10 seconds, say 5 seconds in the presence of 2-10, say 5 moles of hydrogen per mole of hydrocarbon to yield 14.19 parts of lighter gases and 54.0 parts of an aromatic stream in line 42 containing 1278 parts of benzene, 33.61 parts of toluene, 6.37 parts of xylenes and 1.24 parts of C and heavier aromatic. This stream is passed through line 42 and combined with the stream from line 30 into lines 50 and 14 fromwhich it is passed to tower 15. The so-recycled stream in line 50 contains 32.10 parts of benzene, 67.43 parts of toluene, 30.91 parts of xylenes and 7.68 parts of C and heavier aromatics.

It will be apparent to those skilled in the art that practice of the process of this invention permits conversion of 102.5 parts of charge C C aromatics into 87.43 parts of product toluene and that the benzene and C -C aromatic streams may readily be converted to extinction to toluene.

If the 102.5 parts of C ;C were converted to toluene by dealkylation and fractionation only (no transalkylation), the recovery of toluene would be ca 60 parts as compared with 87.43 parts recovered by the process of this invention.

Similarly from a feed containing 94 parts of xylenes can be produced by the process of this invention wherein a portion of the C to C aromatic is partially dealkylated. The benzene and toluene so formed are combined with the benzene and toluene in the feed and transalkylated with i the remaining C C aromatics to generate additional xylenes.

Although this invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention.

We claim:

1. The method of treating a charge monocyclic aromatic hydrocarbon stream containing (1) a monocyclic middle component, (ii) a monocyclic heavier component having a larger number of carbon atoms than does said middle component, and (iii) a lighter component having a smaller number of carbon atoms than does said middle component which comprises:

a. separating said charge monocyclic aromatic hydrocarbon stream into (i) a first stream containing said lighter component, (ii) a second stream containing said middle component, and (iii) a third stream containing said heavier component.

b. dividing said third stream containing said heavier component into (i) first portion containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component and (ii) a second portion containing the remainder of said third stream;

c. transalkylating said first stream containing said lighter component with said first portion of said third stream containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component thereby forming a transalkylate stream containing said middle component;

d. recovering said middle component from said transalkylate stream;

e. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier component, a middle component, and a lighter component; and

f. recovering said middle component from said dealkylate stream.

2. The method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a monocyclic middle component, (ii) a heavier component having a monocyclic larger number of carbon atoms than does said middle component, and (iii) a monocyclic lighter component having a smaller number of carbon atoms than does said middle component which comprises:

a. separating said charge monocyclic aromatic hydrocarbon stream into (i) a first stream containing said lighter component, (ii) a second stream containing said middle component, and (iii) a third stream containing said heavier component.

b. dividing said third stream containing said heavier component into (i) first portion containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component and (ii) a second portion containing the remainder of said third stream;

c. transalkylating said first stream containing said lighter component with said first portion of said third stream containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component thereby forming a transalkylate stream containing said middle component;

d. recovering said middle component from said transalkylate stream;

e. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier component, a middle component, and a lighter component; and

f. passing said dealkylate stream to said separating operation.

3. The method of treating a charge stream as claimed in claim 2 wherein said transalkylate stream is recycled to said separating operation.

4. The method of treating a charge stream as claimed in claim 2 wherein said middle component is recovered from said dealkylate stream prior to passing said dealkylate stream to said separating operation.

5. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains benzene in said lighter component, toluene in said middle component, and xylene in said heavier component.

6. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains C to C aromatic hydrocarbons.

7. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains toluene in said lighter component, xylene in said middle component, and in said heavier component hydrocarbons containing at least nine carbon atoms.

8. The method of treating a charge C C hydrocarbon stream which comprises:

a. separating said charge stream into a benzene stream, a toluene stream, and a C -C stream,

b. transalkylating said benzene stream with a portion of said C -C stream substantially equivalent to 14 said benzene stream thereby forming a transalkylate stream containing toluene; c. recovering toluene from said transalkylate; d. dealkylating the C C from the C C stream, which is in excess of that passed to the transalkylating operation thereby forming a dealkylate stream;

and e. recovering toluene from said dealkylate stream. 9. The method of treating a charge C C hydrocarl0 bon stream which comprises a. separating said charge stream into a benzene stream, a toluene stream, and a C -C stream;

b. transalkylating said benzene stream with a portion of said C -C stream substantially equivalent to said benzene stream thereby forming a transalkylate stream containing toluene;

c. passing said transalkylate to said separating operation;

d. dealkylating the C -C from the C ,C stream,

which is in excess of that passed to the transalkylating operation thereby forming a dealkylate stream containing toluene;

e. passing said dealkylate stream to said separating operation; and

f. recovering toluene from said separating operation.

10. The method of preparing toluene which comprises a. reforming a naphtha thereby forming a reformate;

b. recovering a charge BTX hydrocarbon stream from said reformate;

c. separating said charge stream into a benzene stream, a toluene stream, and a xylene stream;

b. transalkylating said benzene stream with a portion of said xylene stream substantially equivalent to said benzene stream thereby forming a transalkylate stream containing toluene;

c. recovering toluene from said transalkylate;

d. dealkylating the xylene from the xylene stream,

which is in excess of that passed to the transalkylating operation thereby forming a dealkylate stream; and

e. recovering toluene from said dealkylate stream.

11. The method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a monocyclic middle component, (ii) a heavier component having a larger number of carbon atoms than does said middle component, and (iii) a monocyclic lighter component having a smaller number of carbon atoms than does said middle component which comprises:

a. separating said charge monocyclic aromatic hydrocarbon stream into (i) a first stream containing said lighter component, (ii) a second stream containing said middle component, and (iii) a third stream containing said heavier component;

b. combining (i) said first stream containing said lighter component from said separating operation and (ii) a lighter component recovered from a dealkylate stream thereby forming a combined lighter stream;

dividing said third stream containing said heavier component into (i) a first portion containing an amount of said heavier component substantially equivalent to said combined lighter stream and (ii) a second portion containing the remainder of said third stream; (1. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier 16 tion of said third stream containing an amount of said heavier component substantially equivalent to said combined lighter stream containing said lighter component thereby forming a transalkylate stream containing said middle component; and h. recovering said middle component from said transalkylate. 

1. THE METHOD OF TREATING A CHARGE MONOCYCLIC AROMATIC HYDROCARBON STREAM CONTAINING (I) A MONOCYCLIC MIDDLE COMPONENT, (II) A MONOCYCLIC HEAVIER COMPONENT HAVING A LARGER NUMBER OF CARBON ATOMS THAN DOES SAID MIDDLE COMPONENT AND (III) A LIGHTER COMPONENT HAVING A SMALLER NUMBER OF CARBON ATIOMS THAN DOES SAID MIDDLE COMPONENT WHICH COMPRISES: A. SEPARATING SAID CHARGE MONOCYCLIC AROMATIC HYDROCARBON STREAM INTO (I) A FIRST STREAM CONTAINING SAID LIGHER COMPONENT, (II) A SECOND STREAM CONTAINING SAID MIDDLE COMPONENT, AND (III) A THIRD STREAM CONTAINING SAID HEAVIER COMPONENT. B. DIVIDING SAID THRID STREAM CONTAINING SAID HEAVIER COMPONENT INTO (I) FIRST PORTION CONTAINING AN AMOUNT OF SAID HEAVIER COMPONENT SUBSTANTIALLY EQUIVALENT TO SAID FIRST STREAM CONTAINING SAID LIGHTER COMPONENT AND (II) A SECOND PORTION CONTAINING THE REMAINDER OF SAID THIRD STREAM; C. TRANSALKYLATING SAID FIRST STREAM CONTAINING SAID LIGHTER COMPONENT WITH SAID FIRST PORTION OF SAID THIRD STREAM CONTAINING AN AMOUNT OF SAID HEAVIER COMPONENT SUBSTANTIALLY EQUIVALENT TO SAID FIRST STREAM CONTAINING SAID LIGHTER COMPONENT- THEREBY FORMING A TRANSALKYLATE STREAM CONTAINING SAID MIDDLE COMPONENT; D. RECOVERING SAID MIDDLE COMPONENT FROM SAID TRANSALKYLLATE STREAM; E. DEALKYLATING SAID SECOND PORTION OF THE THIRD STREAM CONTAINING SAID HEAVIER COMPONENT THEREBY FORMING A DEALKYLATE STREAM CONTAINING A HEAVIER COMPONENT, A MIDDLE COMPONENT, AND A LIGHTER COMPONENT; AND F. RECOVERING SAID MIDDLE COMPONENT FROM SAID DEALKYLATE STREAM.
 2. The method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a monocyclic middle component, (ii) a heavier component having a monocyclic larger number of carbon atoms than does said middle component, and (iii) a monocyclic lighter component having a smaller number of carbon atoms than does said middle component which comprises: a. separating said charge monocyclic aromatic hydrocarbon stream into (i) a first stream containing said lighter component, (ii) a second stream containing said middle component, and (iii) a third stream containing said heavier component. b. dividing said third stream containing said heavier component into (i) first portion containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component and (ii) a second portion containing the remainder of said third stream; c. transalkylating said first stream containing said lighter component with said first portion of said third stream containing an amount of said heavier component substantially equivalent to said first stream containing said lighter component - thereby forming a transalkylate stream containing said middle component; d. recovering said middle component from said transalkylate stream; e. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier component, a middle component, and a lighter component; and f. passing said dealkylate stream to said separating operation.
 3. The method of treating a charge stream as claimed in claim 2 wherein said transalkylate stream is recycled to said separating operation.
 4. The method of treating a charge stream as claimed in claim 2 wherein said middle component is recovered from said dealkylate stream prior to passing said dealkylate stream to said separating operation.
 5. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains benzene in said lighter component, toluene in said middle component, and xylene in said heavier component.
 6. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains C6 to C11 aromatic hydrocarbons.
 7. The method of treating a charge stream as claimed in claim 2 wherein said charge stream contains toluene in said lighter component, xylene in said middle component, and in said heavier component hydrocarbons containing at least nine carbon atoms.
 8. The method of treating a charge C6-C11 hydrocarbon stream which comprises: a. separating said charge stream into a benzene stream, a toluene stream, and a C8-C11 stream, b. transalkylating said benzene stream with a portion of said C8-C11 stream substantially equivalent to said benzene stream thereby forming a transalkylate stream containing toluene; c. recovering toluene from said transalkylate; d. dealkylating the C8-C11 from the C8-C11 stream, which is in excess of that passed to the transalkylating operation thereby forming a dealkylate stream; and e. recovering toluene from said dealkylate stream.
 9. The method of treating a charge C6-C11 hydrocarbon stream which comprises a. separating said charge stream into a benzene stream, a toluene stream, and a C8-C11 stream; b. transalkylating said benzene stream with a portion of said C8-C11 stream substantially equivalent to said benzene stream thereby forming a transalkylate stream containing toluene; c. passing said transalkylate to said separating operation; d. dealkylating the C8-C11 from the C8-C11 stream, which is in excess of that passed to the transAlkylating operation thereby forming a dealkylate stream containing toluene; e. passing said dealkylate stream to said separating operation; and f. recovering toluene from said separating operation.
 10. The method of preparing toluene which comprises a. reforming a naphtha thereby forming a reformate; b. recovering a charge BTX hydrocarbon stream from said reformate; c. separating said charge stream into a benzene stream, a toluene stream, and a xylene stream; b. transalkylating said benzene stream with a portion of said xylene stream substantially equivalent to said benzene stream thereby forming a transalkylate stream containing toluene; c. recovering toluene from said transalkylate; d. dealkylating the xylene from the xylene stream, which is in excess of that passed to the transalkylating operation thereby forming a dealkylate stream; and e. recovering toluene from said dealkylate stream.
 11. The method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a monocyclic middle component, (ii) a heavier component having a larger number of carbon atoms than does said middle component, and (iii) a monocyclic lighter component having a smaller number of carbon atoms than does said middle component which comprises: a. separating said charge monocyclic aromatic hydrocarbon stream into (i) a first stream containing said lighter component, (ii) a second stream containing said middle component, and (iii) a third stream containing said heavier component; b. combining (i) said first stream containing said lighter component from said separating operation and (ii) a lighter component recovered from a dealkylate stream thereby forming a combined lighter stream; c. dividing said third stream containing said heavier component into (i) a first portion containing an amount of said heavier component substantially equivalent to said combined lighter stream and (ii) a second portion containing the remainder of said third stream; d. dealkylating said second portion of the third stream containing said heavier component thereby forming a dealkylate stream containing a heavier component, a middle component, and a lighter component; e. recovering said middle component from said dealkylate stream; f. recovering said lighter component from said dealkylate stream; g. transalkylating said combined lighter stream containing said lighter component with said first portion of said third stream containing an amount of said heavier component substantially equivalent to said combined lighter stream containing said lighter component - thereby forming a transalkylate stream containing said middle component; and h. recovering said middle component from said transalkylate. 